1. Field of the Invention
The present invention relates to fiber optics and, more particularly, to an apparatus and method for compensating for shift in alignment of optical components after assembly of the optical package.
2. Description of the Related Art
The current explosion in the use of fiber optic technology in telecommunications and data processing is well documented. With this phenomenal technological growth, a wide variety of optical devices have become available. Interconnecting these optical devices, however, has remained a daunting task as such devices require extremely precise mechanical alignment. This problem is most severe for reflective applications, since the error in alignment cannot be greater than a micron.
One available form of optical packaging requires the mounting of optical components in separate metal holders. For example, fiber terminations are mounted in one metal holder and a focusing device such, for example, as Graded Index (GRIN) or conventional lens is mounted in another metal holder; additional optical components are mounted in still further metal holders. The optical components in these different metal holders are optically aligned by sliding the metal holders relative to each other. When proper alignment is achieved, the holders are typically laser-welded together so as to fix the alignment positions of these optical components.
FIG. 1 shows a typical prior art optical package 10 for reflective applications. The package has a dual fiber termination 12 disposed at one end of the package at which the upper fiber 14 is configured as an input to the package and the lower fiber 16 is configured as an output. As shown, the optical signal emitted from the upper fiber 14 is collimated by a double convex lens 18 and directed onto a mirror 20. The mirror 20 reflects the collimated beam back toward the convex lens 18 which then converges the collimated beam onto the lower fiber 16.
The termination 12, and collimating lens 18 and mirror 20 are disposed in separate metal holders 21; the metal holders 21 are laser welded together once the optical components have been optically aligned. Due to mechanical forces arising from the welding process, these optical components, even if perfectly aligned prior to welding, will often experience "post-weld shift," i.e. changes in the relative positions of the metal holders, and thus the components, after welding. Such "post-weld shift" may be in the order of 1 .mu.M or more, depending on various parameters such as the coefficients of thermal expansion of the metal holders and the geometry and arrangement of the weld zones. Although post-weld shift may be acceptable for transmission applications, the shift could be extremely detrimental in reflective applications as it causes unacceptably high optical losses.
For example, a shift of 1 .mu.M between the dual fiber termination 12 and the center of lens 18 in the vertical direction in FIG. 1 will cause the reflected beam to converge at a point 1 .mu.M below the original position of the lower fiber 16. Since the lower fiber 16 has been vertically displaced 1 .mu.M from its original position, the reflected beam will miss the intended target, i.e. the center of the lower fiber 16, by as much as 2 .mu.M. Such misalignment will seriously degrade the performance of the optical package and thus render it unfit for use.
Thus, there is a critical need for an optical package having the ability to compensate for post-weld shifts of optical components.